A spark suppressor circuit of this type is known from French Patent Application 2,626,115. Electrical thermal appliances, such as irons, coffee-makers and cookers, use thermostats to control the temperature. In these thermostats a bimetal operates an electrical switch to interrupt the current to the heating element. In thermal appliances the trend is towards higher power heating elements. The higher power results in a larger current, causing increased wear of the contacts of the electrical switch. The increased wear reduces the lifetime of the thermostat, which may even become less than the life expectancy of the thermal appliance. The wear is caused by sparking between the contacts of the electrical switch at the instants of opening, closing and bouncing of the electrical switch. A spark suppression circuit may be employed to prevent sparking and to increase the lifetime of the electrical switch.
In the known spark suppression circuit the electrical switch is connected in series with an inductive load at the switch terminal. The series connection of the switch and the load is arranged between the first and the second supply voltage terminal, which terminals are connected to an a.c. mains voltage. The first main electrode of the triggerable electronic switch is connected to the switch terminal via a resistor. The trigger gate of the triggerable electronic switch is connected to the first main electrode of the triggerable electronic switch via a threshold device. When the electrical switch opens the interruption of the current through the inductive load causes a voltage increase at the switch terminal, which triggers the triggerable electronic switch, thus temporarily short-circuiting the electrical switch until the next half-cycle of the a.c. mains voltage. A drawback of this known spark suppression circuit is that it is only suitable for use with inductive loads, such as relay coils, transformers and motors. A resistive load, such as a heating element in a thermal electrical appliance will not produce a voltage peak which is sufficiently high to trigger the triggerable electronic switch.